I’d never really thought about this and just got on with cycling, but I guess (as it’s a skill we learn) that it was just about balance and forward momentum; it appears though that science isn’t too sure how we perform this amazing feat.

The BBC’s Terrific Science series of webpages for you people has a ”Things science doesn’t know… Yet!” which includes the following on bicycles:

Bicycles
How does a bike stay upright?

The first modern bicycle was invented by John Kemp Starley in 1885. It can be hard to balance when you are learning to ride and, as you wobble along, you might wonder just how the bike stays stable. Well, it turns out you are not the only one, because scientists don’t quite know how bicycles stay upright.

One theory was that bikes stayed upright because of something called the gyroscopic effect, which is generated by the spinning of the wheels. This effect alone is not powerful enough in a bike to keep it upright, so there must be something else to keep it steady. Engineers currently think that bicycles are kept upright by a complicated feedback system in which there are several different mechanisms interacting with each other. For example, research has shown that cyclists themselves do much of the work, making tiny adjustments and wobbling from side to side, like when you try to stand on one leg.

Again the skill/balance aspect seems obvious to me (trackstands – which I still haven’t learnt to do –  being a case in point and where there’s no gyroscopic force) but I guess it’s a case of scientific proof.

a bit like flying, you have to learn to throw yourself at the ground and miss. physics will temporarily forget about you.

Take the front wheel out from your bike, hold one side of the skewer, it will fall so the wheel is horizontal, now try this again with the wheel spinning, it will stay verticle.

That is the gyroscopic effect and combined with your balance and inate superiority as a cyclist keeps you upright(most of the time).

My bike won’t stay upright. It’s too tired.

….Anyone seen my coat

Gyroscopic precession does have a part to play but most of the time we are riding too slowly for it to have a big effect.

Trail, castor and rake probably has a bigger effect.  I’m sure we’ve all ridden bikes that feel like they want to self-centre without any input.

You think science can’t get it’s head around how we stay upright? Make sure you don’t ask it about steering then. You’ll blow it’s fuzzy little mind.

we stay up by wobbling – this was proved in the UK courts when the defense used by a driver who hit a cyclist was along the lines of ‘he was wobbling’.

just watch a small child learning to ride and you’ll see it

It is sort of interesting but I find how you make a motorcycle go around a corner even interestinger.  I had some training where they used a bike that could have the steering locked straight ahead to demonstrate that you don’t just lean, you countersteer.  Riding in a straight line was OK if a little odd but cornering was very, very limited

A lot of the time I don’t……

(Gyroscopic effect)….most of the time we are riding too slowly for it to have a big effect

But if you get a bike up to speed and jump off (or roll it down a hill) it’ll do a pretty decent job on its own. Whereas resolving vectors, to get only the side to side components unless the bike is perfectly balanced it will fall over immediately. As it does if you try to stand one up without it moving.

So it might be small, and the effect ‘immaterial’ in absolute terms but I reckon gyroscopic effect is the positive equivalent of the straw that broke the camel’s back, on the basis that most people can ride a bike, very few can do a trackstand.

I’ve longed assumed that there are different forces at play when coasting intermittently and no-handed from the pub late at night down a canal towpath.

(defers to Arend Schwab)

Then there’s a unicycle…

surely it’s partly down to rigidity. Why don’t we fall over while walking.. our bones are rigid or lots of them all together gives our body rigidity, the bike is just an extension of this.. ianas

It is sort of interesting but I find how you make a motorcycle go around a corner even interestinger.  I had some training where they used a bike that could have the steering locked straight ahead to demonstrate that you don’t just lean, you countersteer.  Riding in a straight line was OK if a little odd but cornering was very, very limited

You’re likely countersteering on a bicycle too to some extent, though the effect is less pronounced at lower speeds. It’s one of those things that’s very counter intuitive to think about but feels natural when you try it, and seems to be an instinctive part of keeping your balance through a corner.

You steer into the direction that you are falling. Simples. Bicycles cannot move in a perfect straight line, they run in continuous curves. The radius of these curves increases with speed, and eventually appears to become infinite. Your centre of gravity is a pendulum, continuously crossing the centre line. Gyroscopic effects are very modest.

That’s how I teach kids to ride, get them to steer into the fall. Exaggerated movements to begin, then tiny ones. Easiest way is to walk next to them, helping them by moving one end of the bars gently.

Gyroscopic forces have pretty much zero effect on a bicycle staying upright

Even if you cancel them out with a wheel spinning in the opposite direction mounted close to each wheel, bicycles still stay upright.

You’re likely countersteering on a bicycle too to some extent

I’ve noticed on my newer, longer, slacker bike that countersteering is a very useful image to have. I think Pole produced a video on how to steer their long, slack bikes which talks about this too. It is a bit counter-intuitive, but it works.

Getting back to staying upright, I thought it was pretty well established that you simply moved the bike around to keep bringing it back under your centre of gravity i.e. you fall to the right, then move your bike under yourself so you are now on the left of the bike and start falling to the left etc. Same as balancing a broom or pencil on your finger. It is always falling, but you keep moving your finger so that it never actually falls.

I sacrafice a chicken everytime I go out , is that not what everybody does?

Getting back to staying upright, I thought it was pretty well established that you simply moved the bike around to keep bringing it back under your centre of gravity i.e. you fall to the right, then move your bike under yourself so you are now on the left of the bike and start falling to the left etc. Same as balancing a broom or pencil on your finger. It is always falling, but you keep moving your finger so that it never actually falls.

so why is that piss easy for most people to do while the bike is moving along, but when stationary hardly anyone can manage for more than a few seconds?

Gyroscopic effects might be small in absolute terms but do they add just enough to cross the can’t balance / can balance threshold?

You watched this video too? https://www.youtube.com/watch?v=oZAc5t2lkvo

Gyroscopic forces have pretty much zero effect on a bicycle staying upright

Even if you cancel them out with a wheel spinning in the opposite direction mounted close to each wheel, bicycles still stay upright.

^^^^^

I hadn’t Geuben, that it’s really good, thanks!

so why is that piss easy for most people to do while the bike is moving along, but when stationary hardly anyone can manage for more than a few seconds

Because it’s much harder to move the whole bike (contact patches and all) under your centre of gravity if it’s not moving.

If I come to a halt and turn the wheel to the right (say) and then start to fall to the right, it is easy for me to just push on the pedals, ride off and stay upright. But if I fall to the left things get harder as I haven’t perfected the art of moving my bike backwards to get it under my centre of gravity, which is the art of the trackstand.

That Arend Schwab lecture is amazing (not that I understood it all)! I wasn’t even aware of self-stability.

Is there a ‘magic’ speed range within which bicycles remain self-stable then? I’ve never experienced speed wobble (I don’t go that fast) but as I understand it at that point the bike becomes unstable even with a rider.

Getting back to staying upright, I thought it was pretty well established that you simply moved the bike around to keep bringing it back under your centre of gravity

Yes and if you keep moving bars right and left very quickly you r remain stable.  Try it on one of those bikes which move the wheel in opposite direction to steering.  Most people can’t ride them but all you need to do is wobble the bars left and right continuously and it is very easy.  But maybe that’s just me as I can also track stand for hours….

http://cycleseven.org/wp-content/uploads2/Mejinard-et-al.pdf

I think the BBC quote is a bit confused. There’s two separate questions: how do we keep a bike upright, and how can a bike stay upright when there’s no one on it?

I think the first is well understood: you steer the bike to keep the contact patch under your centre of gravity i.e. you’re constantly falling and steering into it.  You can only do this when you’re moving.

The second is partly understood: the handlebars turn themselves automatically in such a way that they steer into any fall.  This is the result of the interaction number of different forces, and the bit that’s not completely understood is exactly which combinations of those forces will result in a stable bike.  If the bars don’t turn enough, it’ll fall over.  If they turn too much, it’ll over-correct and wiggle out of control and fall over.

There’s a middle case which is riding a bike with no hands, which you can do even if the bike itself isn’t stable because you can cause the bars to turn by wiggling your hips.

Track standing is possible if you’re able to move the bike left and right underneath you, which you can do easily enough if you turn the handlebars and can make the bike go forwards and backwards.  Freewheels make that last bit hard, which is why you need either a hill or a fixie.